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FACTOR ANALYSIS TO SUPPORT HIGH-RESOLUTION MAPPING OF SURFACE WATER IN UPPER SÃO FRANCISCO BASIN

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FACTOR ANALYSIS TO SUPPORT HIGH-RESOLUTION MAPPING OF SURFACE WATER IN
UPPER SÃO FRANCISCO BASIN

Machado, DV1; Marques. ED2; Amarante, RT3; Viglio, EP2; Santos, EAM2; Silva Júnior, GC4; Silva-Filho, EV1

1Universidade Federal Fluminense, 2Serviço Geológico do Brasil, 3ITV-Vale, 4Universidade Federal do Rio de Janeiro

Abstract The World Health Organization estimates that water scarcity will increase in certain regions due climate change and population growth. High-resolution mapping and data integration by fator analysis has proven to be an important and effective tool for identifying and assessing the quality to support for water management. The Upper São Francisco Basin (233,564 km2) encompasses the largest karst area in the country and includes the biomes Cerrado (woodland savana), Atlantic Forest (rainforest), and Caatinga (dry forest). About 49% of the region is covered by forest, while 51% is covered by agriculture and other uses. In this study, the chemistry of surface water during the dry season was analysed in 1,418 small rivers and streams. They were analysed for physico-chemical parameters, cations, anions, and metals. The database belongs to the Geological Survey of Brazil. The collecting sampling followed a systematic proceeding based on the regional distribution of samples, englobing maximum área to better represent the results. This study presents the results of the basin’s first high-resolution regional mapping. Factor Analysis was used to integrate and enhance the understanding of natural and anthropogenic processes and to support the analysis of hydrogeochemistry data. Varimax rotation and factor extraction method based on principal components was employed. The centred log-ratio transformation was used to reduce the closure effect and the incidence of spurious correlations. The result was based on the correlation and the values of the significant loadings were considered > 0.45 for positive loadings and < -0.45 for negative loadings. Four factors were generated, accounting for a cumulative variance of 61.24%. Factor 1 (22.68%) showed an association which corroborate the carbonate dissolution, especially in the northern section. This region corresponds to the main outcropping karst areas in Brazil, highlighting the influence carbonate outcrops from the Bambuí Group. The Factor 2 (15.50%) showed two associations. Positive significant loadings interpreted by domestic influences and industrial activities. Significant negative loadings corresponding to chemical weathering of silicate lithotypes. Factor 3 (12.36%) showed association in the positive significant loadings suggesting soil erosion and leaching in agricultural areas. Factor 4 (10.71%) shows a positive loading correlation that suggesting a dissolution of feldspars. The integration of the results suggests that many of the microbasins analysed are effected by human activities, particularly large-scale agriculture. Changes in surface water quality not only affect the health of the ecosystem, but also impact human health.

Key-words: Chemical elements sources, factor analysis, water management, São Francisco river basin.

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Key-words: Chemical elements sources; factor analysis; water management; São Francisco river basin.